Knowledge concerning the regulation of arterial blood pressure holds importance beyond basic scientific interest. The alterations in this basic pressure control system which occur in the very common disease process of hypertension can only be understood on the basis of our understanding of how arterial pressure is normally regulated. There are numerous mechanisms within the organism which contribute to the control of arterial blood pressure and it is important to know how much contribution each of these pressure control systems makes to the total body regulation. Quantitative data has not been available to permit the determination of the overall importance of many of these hormonal systems of blood pressure regulation. Studies which we have conducted in our laboratory have determined the relative importance of the renin-angiotensin-aldosterone system in the short-term control of arterial pressure under certain conditions. The general rationale of the studies which are presently being conducted in this laboratory is to quantitatively evaluate the role of this and other hormonal systems in the acute and long-term control of arterial pressure. This includes all systems which importantly influence arterial pressure such as the control of body fluid volumes which are importantly influenced by renal function in such hormones as the antidiuretic hormone, angiotensin, and aldosterone. The studies are also designed to determine the relative importance of specific factors known to alter the overall capability of the individual systems to control pressure. The experiments being conducted are therefore designed to obtain quantitative data so that the relationships between the components of the systems can be represented mathematically and modeled on a digital computer to precisely test against experimental results obtained in the laboratory. Computer models yield a better understanding of the interactions within the system and frequently predict unexpected results not yet observed experimentally, which in turn generate new experimental protocols.